Unlike arches, which carry loads in compression, beams and lintels act as flexural members spanning horizontally between supports. Lintels usually are smaller members spanning and carrying only the loads immediately above window and door openings. Lintels must resist compressive, bending, and shear stresses.
Lintels must be designed to carry their own weight, plus the weight of the masonry inside the triangle formed by the line of arching action. Arching action produces a horizontal thrust at each abutment. The abutments, therefore, must have enough mass to resist this force.
Structural steel shapes are commonly used to span openings in brick masonry. Steel angles are the simplest shapes and are suitable for openings up to 8 feet wide, where superimposed loads are no more than 5,000 pounds per lineal foot. For wider openings or heavier loads, steel beams with suspended plates can be used. Openings in concrete masonry walls are spanned more commonly with U-shaped lintel blocks, reinforced with deformed steel bars and grouted.
Building movement must be considered in any type of construction, and exterior walls are particularly subject to differential thermal, moisture, and structural movements. To be most effective, movement joints should separate the masonry carried by the lintel from that in the adjacent wall. This ordinarily means locating them at the end of the lintel.
Thermal and Moisture Protection
Since any opening in a wall is an opportunity for a leak, moisture protection at lintels is critical. Flashing should be located above reinforced masonry lintels as well as steel lintels.